Biologist Finds Silver Lining In Listeria Outbreak

Jan 28, 2016

Credit Grant /

An outbreak of Listeriosis has killed one person in Michigan and hospitalized 11, including a person in Indiana. But that bad news might provide researchers with more information to better detect future problems.

The Centers for Disease Control and Prevention has linked the strain to a Dole packaging plant in Ohio. Many people hit by the outbreak reported eating bagged salads originating at the factory.

The government is recommending grocers and restaurants who use the salad mixes rid themselves of the contaminated products.

Purdue microbiology and food science professor Haley Oliver calls Listeria a “farm-to-table” pathogen that can get mixed up in the food supply at any point in the food packaging process because it’s found in soil.

“So we can go out in the dirt and we can find that organism it finds it’s found its way into a human host mostly by accident,” she says. “It’s not a very good pathogen at the end of the day…but it’s not something we’re going to eliminate from the surface of the earth.”

Indiana State Epidemiologist Pam Pontones explains doctors are required to report certain diseases, including Listeriosis, to the local and state health departments. Then begins the analysis:

"[We ask] where that person or how that person may have been exposed?” Pontones asks. “What the disease agent may be? Do we need to get more information, are we missing anything?”

They report their findings to the CDC, which looks for patterns. That’s how this particular outbreak was traced to the salad facility.

Pontones says no new cases of the disease have been reported in the state.She notes a clustered outbreak is somewhat unusual.

"Typically, Listeria cases are sporadic, which means they’re not linked to one another,” she says.

Oliver says the majority of Listeria outbreaks have been traced to deli meats.

Because they were making up the vast majority—90 percent—of the Listeria cases historically, there really hasn’t been a focus on some of the other food vectors, like produce,” she says.

Oliver says the there is a silver lining to the outbreak – it increases awareness about different and under-researched agents of contamination, such as lettuce.

The first cases were reported last summer, but it took the CDC months to compile enough data to spot a pattern linking the strain to the Dole facility.